In electronic photography, application devices, primarily semiconductor laser diodes, He-Ne lasers, emission diodes, and so forth are used. Since these optical sources produce long wavelength light, from 630 nm to 800 nm, photosensitive material for electronic photography generally is of the multilayer, function separating type. Such photosensitive material generally comprises a carrier generation layer consisting of a selenium/tellurium alloy of high tellurium concentration having high sensitivity in even long wavelength optical regions, a carrier transport layer consisting of a selenium/arsenic alloy for transporting carriers (positive holes) generated in the carrier generation layer to a conductive substrate, and an overcoat layer for protecting the carrier generation layer from external stress. Although with high arsenic concentrations, the friction-proof properties and heat-proof properties of the overcoat layer are improved, the dark decay and fatigue characteristics deteriorate.
As one means for solving such problems Japanese Patent Application Laid-Open No. 112250/1989 discloses insertion of a carrier injection preventive layer consisting of pure selenium or a selenium/arsenic alloy of low arsenic concentration (less than 10% by weight) between a carrier generation layer consisting of a selenium/tellurium alloy of high tellurium concentration and an overcoat layer. A photosensitive material having an overcoat layer with improved friction-proof and heat-proof properties can thereby be obtained.
Amorphous silicon material and amorphous silicon nitride are used as highly friction-proof overcoat layer materials. Japanese Patent Application Laid-Open No. 81367/1988 discloses the use of amorphous boronitride as a friction-proof overcoat layer, while Japanese Patent Application Laid-Open No. 81430/1988 similarly discloses the use of amorphous silicon nitroxide.
Photosensitive material comprising a carrier injection preventive layer consisting of pure selenium or a selenium/arsenic alloy, a carrier generation layer consisting of a selenium/tellurium alloy, and an overcoat layer consisting of a selenium/arsenic alloy of high arsenic concentration shows favorable dark decay and fatigue characteristics at room temperature. However, the performance thereof becomes insufficient at high temperatures; namely dark decay and fatigue increase at high temperatures.
In addition, since glow discharge is used to form the surface protective layer when material other than a selenium/arsenic alloy is used for this purpose, a long processing time is required and the cost of the photosensitive material therefore increases.